Master cylinder structure



April 3, 1951 A. B. SEPPMANN 2,547,233

MASTER CYLINDER STRUCTURE Filed Oct. 14, 1947 Patented Apr. 3, 1951 UNITED smrE-s PATENT OFF-ICE animal-[mower 14; ic-im-serialiivb. .v'vasss Claims. I (elite- 5136) 1 I his invention relates to a master cvlinder .structureof the single acting high power ty'p'e wherein the brakes when applied are held in applied position until the' brake pedal is release'd. I one oloject of the invention is to provide a master cylinder of simple, durable'and inexpensive construction which is particularlyadapted for trailers and the like and wherein application of, the lirakesireslilts in the brakes holding even .throjigh pressure "is partially 'let up on the brake pedal, the'brake..pedal being fully releasedfor permitting the 'brakesto return to their nonaPf IieCIZposititSn. I I

Another object istoprovide a master cylinder having 'a relief valve to prevent excessive pressurfes in thefhydraulicfsystem, the brake piston beiiig c'datilole therewith"to open the Same "for '1tufni'fl6w of fl iiid' di'rect ly to the reservoir when thefh'rake pedal 'isj'infits fully released position. I

Still "anotherfofbj'ect is to provide afchec'k 'valve between a "master cylinder and thehydraulic line tofthe lcrakesfto prevent return flow of brake nmmnnm fthebrakes to t h e' cylinder, 'th'e piston try of'ad'ditional "fluid from the reservoir upon rtial release of the brakepedal andre-appli- "cation of the hi-hikes, thus pumping additional .fll ntosthe, hydraulicsy stem to' 'securesufficient "22k ,action Wh'nth'e firststroke6fthepiston r d -H c 4 A further object is to provide a relief valve 'hic isfno'i nially' ireeflfor fiuidftransfenbetween th I hydraulic line and the I reservoir, 'a ndwhich isft'e "soon as the brakeflpedal' is depressed "slightly.

j Withtliese and other "objects inview, my; in- ."verition' consi'sts in the construction, arrange- I Im'e nt and combination of the varioilsfparts of my device wherebytheobjects' contemplated ar'e 'attaihed, as hereinafter more fully set forth, ipointedi out in .my' claims and illustrated in the "'acqompanyingflrawing,'wherein: I I I I 'Ffi'g'u'fe" 1 is averticaljsectional viwfthrodgha cylinder structureerjnbodying' my present sionedto operatein its relief capacitvas' dlthe"cylinder'being'of the type thatpermits oi the reservoir is closed by means of "a closure Lplug (waving avent I 6 to atmosphere.

I ApistonI'Bisslidabl'einthe cylinder land has a rearw'ard"iterision'ilil. 'Thepiston l8"has thereagains't a se'a1ingfcup"20 retained in'position by a spring 34. The rear end of the exftension 'lB has a'se'aling 'cupfltand is socketed to receive the forward "end of an operating -rod 24 extending from 'thebrakepedal. closure disc 26"is held inp'o'sition by"a"retainer 'ring '28 and serves as 'a stop'ior thepist'oh -'IB in the normal position of "Figure 1; I

A closure'plug 3'llfis provided for the'iorward end of th'e' cylinder I-U'anda stopI'pin- 32 is carried "thereby to limit the inward "movement of the piston It; a'si'n Figure 2.

I Apasfsag'eway 36 leads from the cylinder Ill to "a pasjsag'eway 3 8,"a valveseat lfl being interposed'between "the two. ball ty 'e check valve 4'2jisnormallyseated on the-seat Ml by a "spring '62. I

I "The passageway 38 "communicates with -a "'cavityJ lclosed by'a plugifi with which 'the 'hy'draulic line tothe brake is connected. This line is indicate'det "58. A retafder valve is "mounted in the cavity and consists of a seal- "in' washermi having' a metallic 'insert 41 with a spring 54 interposed between this insert and-the bottom of'the cavity. The spring "54 normally seatsthe washer lit-on the inner end of the 'r 'u .1 .6-. a

Ava1ve"stem '50 'exten'ds through the central opening of the washer "46 and has a valve disc 48 normally;seated against the outer face of the 35 fwasher by a spring-"53 interposed between the inner fac'eof the'washer and a di'sc'52 secured to-the inner end of the stem' BO.

The ball is ldcated' in anenlargement 31 of the pais'sageway'tfi and the spring fiz is 'backedby "afiplng 6'3 threaded into-the enlargement 'of' the passageway. Theplug'GShaS a-valve' sea-664 on which a reliefvalve E6 is at times seated. "Such seating as'shown in Figure 2 isefiecteol by a pin 68 carrie'dbya lever 12 -1':)ivotedat 14 "to abracket l6.

' 'The'pinfifl has a threaded portion 'lfl a'djustable in the lever; and alockmut 181s provided toretain the adjustment. The lever 12 is provided with an 'openingf13 which 'surrounds-"a'studllfl having a spring ti lthereoninterposed between a washer I5 andanadjusting nutllz-forthe' tension of the spiin'g"84, I II I I j A"port" ,88"a fiords*communication between the "interior 'of'the' reservoir II! and the interior of the "fc'jrli'n de'r l0. 'Thel lever "12has an ezitension lili to be engaged by a truncated cone shaped portion 90 of the piston I8 which acts asan actuating cam for the lever 12 as will hereinafter appear.

The piston I8 is provided with bypass ports 92 that permit flow of brake fluid from the cylinder back of the piston to the back of the cup and then around its peripheral flange upon the return stroke of the piston l8 caused by the spring 34 when pressure is let up on the brake pedal.

Practical operation In the operation of my master cylinder, when the brake pedal is depressed it will move the actuating rod 24 in the direction of the arrow in Figure 2 which will likewise move the extension I9 and the piston [8 in the same direction. This displaces brake fluid (not shown as it would be confusing on the drawing) in the cylinder l0 ahead of the cup 29 through the passageway 36 past the valve seat 40 by lifting the ball 42 therefrom and through the passageway 38 into the cavity 44, the parts being in the position shown in Figure 2. The pressure of the brake fluid on the inner face of the valve disc 48 opens it as shown so that the fluid can flow through the hydraulic line 58 to the brakes.

The brakes can be applied to the degree desired and then pressure can be let up on the brake pedal and the brakes will remain in the applied position and to that same degree because return flow of fluid is blocked by the check valve 42 and by the relief valve 65. Any time the pressure exceeds that for'which the spring 84 is set however the excess pressure while applying the brakes will be relieved past the relief valve into the reservoir at any time the fluid pressure exceeds the setting of the relief valve. Thus protection is afforded against excess pressure that might rupture the hydraulic system beyond the master cylinder.

The possibility of the brakes holding even when pressure is let up on the brake pedal makes the braking action less strenuous to the driver as he can apply the brakes to the desired degree without manually holdin the brake pedal at that position to maintain the pressure in the hydraulic line. Any pressure that is built up in the line by forward movement of the brak pedal is automatically held so that he can let up on the brake pedal and has to hold it only against the force of the spring 34. Then when it is desirable to release the brake he lets up on the pedal all the way and the cam 90 raises the lever 12 for permitting the relief valve 65 to open and thereby permit the brake fluid to return freely to the reservoir I2.

Such return operates the retarder valve in the usual manner, that is it forces the washer 46 back against the tension of the spring 54 to permit the fluid to flow around the edge of the washer 46 and its metallic insert 41. .a ring with a plurality of spaced curved prongs around its periphery to provide a seat for the ,spring 54. The prongs are guided by the interior The insert is in the form of wall of the cavity 44 while the periphery of the insert is spaced inwardly therefrom to permit free flow of fluid around the insert. This retarder valve however forms no part of my present invention.

By designing the parts of the master cylinder as disclosed I utilize the relief valve itself as a return valve to bypass brake fluid from the hydraulic line to the reservoir past the check valve 42, and the space in the cylinder l0 ahead of the piston 58 is always automatically re-charged with fluid upon the return stroke by reason of atmospheric pressure forcing fluid from the reservoir l2 through the passageways 92 and past the peripheries of the cup 20 while the spring 34 is operating to return the piston to its initial position.

The arrangement is also such that additional brake fluid can be pumped into the system when the initial brake movement is insufficient to apply the brakes to the desired degree. The check valve 42 acts in this case to prevent return flow of brake fluid when pressure on the brake pedal is let up and another charge of liquid is then trapped ahead of the piston l8 during the return movement of the brake pedal nearly to the initial position. The brake pedal of course should not be let up enough for the cam 90 to swing the lever 12 to the position of Figure 1; otherwise the pressure in the brake line will be lost. On the second stroke the trapped liquid ahead of the piston is pumped into the brake line for additional braking effect and the pumping action can be repeated if necessary.

, Some changes may be made in the construction and arrangement of the parts of my device without departing from the real spirit and purpose of my invention, and it is my intention to cover by my claims any modified forms of structure or use of mechanical equivalents which may be reasonably included within their scope.

I claim as my invention:

1. A master cylinder structure comprising a cylinder, a reservoir surmounting said cylinder, a piston in said cylinder, said reservoir having a port communicating said reservoir with said cylinder back of said piston, a return spring for said piston, a passageway communicating with said cylinder in front of said piston, a hydraulic brake line connected with said passageway, a check valve in said passageway opening from the cylinder and toward the brake line, a relief valve from said brake line to said reservoir, means to render said relief valve inoperative comprising a lever pivoted in said reservoir and engaging said relief valve, a spring coacting with said lever to cause said relief valve to engage its seat, said lever having an extension through said port, and said piston having a cam portion cooperable therewith to move said lever against the bias of said last spring, said first spring being stronger than said last spring.

2. A master cylinder structure of the character disclosed comprising a cylinder, a piston in said cylinder, a reservoir communicating with said cylinder back of said piston, a passageway communicating with said cylinder in front of said piston, a hydraulic brake line connected with said passageway, a check valve in said passageway opening from the cylinder and toward the brake line, a relief valve from said brake line to said reservoir, means to render said relief valve inoperative comprising a lever engaging said relief valve, a spring coacting with said lever to cause said relief valve to engage its seat, said lever having a portion in said cylinder, and said piston having a cam portion cooperable therewith to move said lever against the bias of said spring.

3. A master cylinder structure of the character disclosed comprising a cylinder, a reservoir surmounting said cylinder, a piston in said cylinder, a passageway communicating with said cylinder in front of said piston, a hydraulic brake line connected with said passageway, a check valve from said cylinder to said brake line, a relief valve from said brake line to said reservoir, said relief valve being operatively engaged by said piston upon its return to normal position forautomaticallyrendering said relief -.valve inoperative,

and permits flow of fluid past the piston on the return stroke, a hydraulic brake line communieating through said body with the outlet side of said cylinder bore, a check valve therein to hold the hydraulic pressure in the brake line, and a bypass valve for said check valve operable to bypass fluid directly from the outlet side of said check valve to said reservoir, said piston, in its fully retracted position only, effecting opening of said bypass valve.

5. A master cylinder structure comprising a cylinder, a piston therein of the type which traps fluid ahead of the piston on the forward stroke and permits flow of fluid past the piston on the return stroke, a hydraulic brake line communicating with the outlet side of said cylinder, a 20 check valve therein to hold the hydraulic pressure in the brake line, and a bypass valve for said check valve operable to bypass fluid from the brake line to said reservoir, a spring biased element for engaging said bypass valve to normally close it, said element being engaged by said piston upon full release of the brake pedal to permit openin of said bypass valve, said piston disengaging said element whenever said brake pedal is moved away from its full release position so that said element will engage said bypass valve under the bias of the spring for the element to cause the valve to serve as a pressure limiting valve for the brake line whenever such pressure exceeds the setting of the pring.

ALFRED B. SEPPMANN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,147,579 Trego July 20, 1915 2,000,187 Oliver Ma 7, 1935 2,081,056 Loweke May 18, 1937 2,161,304 Loweke June 6,1939 2,242,676 Jurs May 20, 1941 

